Person working as a Software engineer in an MNC is an employee while the chap cleaning the same office is called a worker. Conventionally, both of these classes are recognized as White collar & Blue collar workers respectively. These terms reflects the designations and more specifically their work profiles. The white collar worker works behind the desk, on executive post and with little or no manual work. While the blue collar worker are the true 'working class' and totally into manual work. The term originates from the western world where the typical worker usually wear overalls, jeans or durable work shirts- mostly in the color blue, to more easily cover the dust & dirt they inevitably come into contact with.

(1) Blue collar vs White collar- http://bit.ly/2Xi6a0w

(2) How these terms evolved-http://bit.ly/2IDVtRF